A roundhouse is a type of house with a circular plan, usually with a conical roof. In the later part of the 20th century, modern designs of roundhouse eco-buildings were constructed with materials such as cob, cordwood or straw bale walls and reciprocal frame green roofs.

Roundhouses were the standard form of housing built in Britain and Ireland from the Bronze Age throughout the Iron Age, and in some areas well into the Sub Roman period. The people built walls made of either stone or of wooden posts joined by wattle-and-daub panels, and topped with a conical thatched roof. These ranged in size from less than 5m in diameter to over 15m. The Atlantic roundhouse, Broch, and Wheelhouse styles were used in Scotland. The remains of many Bronze Age roundhouses can still be found scattered across open heathland, such as Dartmoor, as stone 'hut circles'.

Early archeologists determined what they believed were the characteristics of such structures by the layout of the postholes, although a few timbers were found preserved in bogs. The rest has been postulated by experimental archaeology, which has tried different techniques to demonstrate the most likely form and function of the buildings. For example, experiments have shown that a conical roof with a pitch of about 45 degrees would have been the strongest and most efficient design. According to Peter J. Reynolds fire would have been lit inside for heating and cooking, there could not have been a smoke hole in the apex of the roof, for this would have caused an updraft that would have rapidly set fire to the thatch. Instead, smoke would have been allowed to accumulate harmlessly inside the roof space, and slowly leak out through the thatch. However, modern reconstructions of ancient roundhouses are ultimately based on a number of assumptions made by archaeologists which might make reconstructions quite different to the original.

Many modern simulations of roundhouses have been built, including:

Much of the earlier supposition was confirmed or denied at a stroke by the finding of a set of Bronze Age roundhouses at the archaeological dig at Must Farm in Cambridgeshire, UK, where samples of all the materials, from posts to walls, to roof were all found, collapsed and charred, but still in situ after 3,000 years.

That Roundhouse is an early example of a modern roundhouse dwelling which was built in Pembrokeshire Coast National Park, Wales without planning permission as part of the Brithdir Mawr village which was discovered by the authorities in 1998. It is constructed from a wooden frame of hand-cut Douglas Fir forest thinnings with cordwood infill, and reciprocal frame turf roof based on permaculture principles mainly from local natural resources. It was subject to a lengthy planning battle including a court injunction to force its demolition before finally receiving planning approval for 3 years in September 2008.

Irish crannógs were roundhouses typically built on an artificial island in a lake, bog, or estuary. Reconstructions of crannógs can be seen in Craggaunowen, the Irish National Heritage Park, and in Wexford, Ireland.

Circular thatched huts similar to British roundhouses were constructed by Bronze Age and Iron Age cultures in Italy, notably by the Villanovan culture and the related Latial culture associated with the early Latins and Romans. A similar hut representing the 'Hut of Romulus' (Casa Romuli), the supposed home of the legendary founder of Rome, was maintained on the Palatine Hill in the centre of Rome throughout the Republic and Imperial periods.